function p = psd(sig, fftlength, powernormconst)
% power_spectral_density = psd(sig, fft_length, power_normalization_constant)
%
% psd takes a signal and computes its power spectral density.
% This is done by first computing its fft, squaring its
% magnitude, changing to decibels, and adding a constant
% for power normalization.

p=powernormconst+10.*log10((abs(fft(sig,fftlength))).^2);